La Fossa cone is an active stratovolcano located on Vulcano Island in the Aeolian
Archipelago (southern Italy). Its activity is characterized by explosive phreatic and
phreatomagmatic eruptions producing wet and dry pyroclastic surges, pumice fall
deposits, and highly viscous lava flows. Nine 2-D electrical resistivity tomograms (ERTs;
electrode spacing 20 m, with a depth of investigation >200 m) were obtained to image the
edifice. In addition, we also measured the self-potential, the CO2 flux from the soil, and the
temperature along these profiles at the same locations. These data provide complementary
information to interpret the ERT profiles. The ERT profiles allow us to identify the main
structural boundaries (and their associated fluid circulations) defining the shallow
architecture of the Fossa cone. The hydrothermal system is identified by very low values of
the electrical resistivity (<20 W m). Its lateral extension is clearly limited by the crater
boundaries, which are relatively resistive (>400Wm). Inside the crater it is possible to follow
the plumbing system of the main fumarolic areas. On the flank of the edifice a thick layer of
tuff is also marked by very low resistivity values (in the range 1–20 W m) because of its
composition in clays and zeolites. The ashes and pyroclastic materials ejected during the
nineteenth-century eruptions and partially covering the flank of the volcano correspond to
relatively resistive materials (several hundreds to several thousands W m). We carried out
laboratory measurements of the electrical resistivity and the streaming potential coupling
coefficient of the main materials forming the volcanic edifice. A 2-D simulation of the
groundwater flow is performed over the edifice using a commercial finite element code. Input
parameters are the topography, the ERT cross section, and the value of the measured
streaming current coupling coefficient. From this simulation we computed the self-potential
field, and we found good agreement with the measured self-potential data by adjusting the
boundary conditions for the flux of water. Inverse modeling shows that self-potential data
can be used to determine the pattern of groundwater flow and potentially to assess water
budget at the scale of the volcanic edifice.